Alright so Valve hasn't released the L4D SKD yet so this is tricky but people have indeed igued out how you can play through the oiginal L4D campaigns using L4D2 with the new infected and the baseball bat as a melee. Since the SDK isn't released beware it's kind of tricky but the rewards are pretty damn awesome and badass. Here's a link if you are up for it, you also DO need the original L4D to bring over the some of the files. Also you have to play with the new survivors through them, however the point is you DO have the campaigns, here's the link:

http://www.l4dmods.com/index.php?option=com_content&view=article&id=288:how-to-resurrect-the-original-left-4-dead&catid=2:news&Itemid=13

There is a link to the instructions in it as well.

I saw this the other day, though I haven't tried it yet.

Hopefully Valve will release an update to L4D2 with this for L4D1 owners, but this will do for now!

Indeed, I really don't see why not.... the game is more or less an expansive expansion pack, if they had labeled it as an expansion pack then they wuld have actually beaten out Blizzard and D2:LoD as best expansion pack value ever.

I'm tempted to do this because that's still 4 pretty well done campaigns. Wish you could use the old survivors since heir banter was pretty good too. I doubt the new ones have it.

it looks more than expansion pack now, i am downloading the demo now on steam.